Number Systems (Part II): Divisibility, Prime Numbers, and the Structure of Mathematical Division
Primes (greater than 1 with no divisors besides themselves; 2 is the only even) and composites underpin divisibility tests—like sum of digits for 3/9, last digits for 2/4/5/10, or alternating sums for 11—while co-primes (HCF=1) enable factorization for composites like 15=3×5. Trailing zeros in products/factorials count min(2s,5s) via prime factors, revealing how primes structure numerical decomposition for efficient problem-solving.









